Plant

Infection spread through the plant to the hypocotyl that pinches off causing plant death, or ring-bark the stem causing the top to snap off

Leaves have round to irregular creamish-grey lesions with black fruiting bodies. These also occur on varieties with adult blackleg resistance.

After stem extension, internal blackening at at the base of the stem causes yield loss without external signs. With very severe infection dark cracked cankers from internal infection cause plants to lodge with premature death. and shrivelled seed.

White or grey, round to linear lesions with black specks and a dark rim may occur on the surface of the stem.

Pale lesions with a purplish rim on petioles cause pod death or similar lesions on pods that cause seed death under the lesion.

Once the lesion has formed, the fungus grows within the plant’s vascular system to the crown where it causes the crown of the plant to rot, and the plant may snap off and die.

Less severe infection will result in a cracked canker at ground level that restricts water and nutrient flow within the plant, causing it to lodge and mature prematurely.

Blackleg symptoms have also been found in the plant roots, that causes the entire plant to die prematurely.

Management strategies

Seed dressing fungicide

Resistant varieties

Foliar fungicide at the 6 leaf stage can slightly reduce loss, but is not generally economic, particularly in the absence of fungicidal seed treatments.

Fungicide seed treatments, are effective but can not totally prevent yield loss.

Relying only on fungicides to control blackleg poses a high risk of fungicide resistance. Choose a cultivar with adequate blackleg resistance for your region.

If your monitoring has identified yield loss and you have grown the same cultivar for three years or more, choose a cultivar from a different resistance group.

Never sow your canola crop into last year’s canola stubble

How can it be monitored?

As blackleg is capable of overcoming genetic resistance, it is important to monitor crops and manage according to guidelines in the current version of the GRDC blackleg management guide.

Sample crops annually anytime from the end of flowering to windrowing (swathing).

Pull 60 randomly chosen stalks out of the ground, cut off the roots with a pair of secateurs and, using the reference photos in the GRDC blackleg management guide, estimate the amount of disease in the stem cross-section. Yield loss occurs when more than half the cross-section is discoloured.